Choosing a Permanent Irrigation System

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After you've decided to invest in a permanent irrigation system, you have to decide what kind to get. Unfortunately, irrigation systems don't come in a nice tidy box with all the parts and instructions and special tools, as if you were buying a piece of furniture. Instead, you have to design the system to fit your particular situation, and then you have to build it from hundreds of parts gathered up from bins at the irrigation supply store. It's challenging, but anyone can do it. Your first step is to figure out where you'll be using sprinklers and where a drip system would be a better choice. In the following sections, I give you the ins and outs of the different approaches.

Sprinkler systems: Spritzing water everywhere

Sprinklers are generally more wasteful than drip systems (which I cover in the next section) because they apply water in less efficient ways. However, they still have a place in the sustainable landscape. Overhead sprinkler systems are designed primarily for watering lawns, which need even, shallow water delivery. They're also used for ground covers, flower beds, and similar large areas of relatively shallow-rooted plants. (Note: A permanent sprinkler system is buried in the ground. The term overhead refers to the fact that sprinklers spray water into the air rather than applying it directly to the soil, as a drip system does.)

Sprinkling by design

A typical permanent sprinkler system consists of heads that either pop up from the ground or are fixed on plastic risers. The heads are connected by an underground network of pipe and are controlled by a manual or electric valve. When the system is in operation, arcs of water squirt out of each head, spraying the irrigated area from several directions for better coverage.

Benefits and drawbacks

The following are some advantages of permanent overhead sprinklers:

  • Water application is visible (and quite attractive to watch).
  • Foliage gets washed off during irrigation.
  • You can use the system to wash fertilizer into the soil.

Here are some disadvantages of permanent overhead sprinklers:

  • They're susceptible to wind drift, runoff, evaporative loss, and misting, all of which waste water.
  • Coverage is about 70 percent accurate at best, resulting in overwatering to compensate for dry spots, which wastes water.
  • Sidewalks, driveways, houses, cars, slow-moving pedestrians, and domestic animals often get watered too. They seldom benefit.
  • Runoff wastes water and can make pavement dangerously slippery.
  • Overhead watering brings up lots of weeds.
  • Impact-type heads can be noisy.
  • Sprinkler heads can be trip hazards if they're installed near traffic areas.

Drip irrigation: A smarter way to water

Permanent sprinklers are being displaced more and more by drip systems, which greatly reduce water use. A drip system is made up of flexible polyethylene pipe, usually installed on the surface of the ground and covered by mulch, with small drip emitters that are either plugged into holes punched in the tubing or molded directly into it. (The latter type is much more durable and easier to install.)

Drip irrigation is controlled with a manual or automatic control valve the same way as an overhead sprinkler system. But it has two additions: a small filter to prevent dirt and other particulate matter from plugging the emitters and a small pressure regulator to reduce the pressure, which prevents the tubing from blowing apart. Chapter 8 provides info on designing an efficient drip system.

To drip, or not to drip: The good and the bad

Here are the advantages of a drip system:

  • Direct application of water into the soil results in little or no runoff, no spray drift, and consequently no wasted water or safety problems.
  • Drip systems are nearly 100 percent efficient, delivering all the water to the root zone of the plants in an even pattern throughout the area.
  • Because most of the soil surface remains dry, you'll have fewer weeds.
  • Most plants really love being drip-irrigated and respond with strong, healthy growth; sturdy root systems; and reduced disease problems.
  • The system is invisible and silent when it's in operation.
  • No trenching is required to install a drip system.
  • Costs of materials and installation are comparable to (or lower than) those of a sprinkler system, and your water bill will be smaller.

These are the disadvantages of a drip system:

  • Drip tubing can be damaged by careless digging, rodents, vandalism, and foot traffic.
  • You can't see or hear a drip system working, so you can easily forget to turn it off if you have a manually operated system. You can set a timer to remind you, of course, or automate your system (see the section on automatic irrigation controllers later in this chapter).
  • A drip system won't wash fertilizer into the soil. Instead, when you apply fertilizer, you have to water it by hand or with a portable overhead sprinkler, or you can apply it just before a good soaking rain.
  • Drippers don't wash off foliage or keep mulch moist. It's a good idea to supplement drip irrigation with an occasional overhead watering, if only to keep things clean. Cleanliness isn't just for the sake of appearance; photosynthesis works better when plant leaves are free of dust and dirt.

Misconceptions about drip

If you talk to enough people in the landscaping business, sooner or later you'll run across an anti-drip zealot who jumps up and down about how bad drip systems are. No offense to these well-meaning people, but they're very wrong about drip. They usually don't understand how drip works, or they've installed systems poorly and have suffered the consequences.

Here are some of the misconceptions about drip and why they're wrong:

  • Drip doesn't last. Poorly installed systems of any kind don't last. But drip tubing is made of polyethylene, which will endure far longer than us, our gardens, and probably civilization itself. Unless it's damaged, your drip system won't have longevity problems.
  • The emitters plug up. If you've installed a proper filter, the tiny particles that get through it will also get through the emitters, because their openings are bigger than the openings in the filter. If you keep your filters in good shape by periodically cleaning them and replacing damaged inserts, you'll never have a problem with plugging.

The one exception is the nasty problem called bacterial iron slime, which can grow in emitters and quickly plug them. See Chapter 8 for info about identifying bacterial iron slime.

✓ Drip doesn't cover properly. Use the grid system to water entire root zones. This method is the solution to the coverage problem, and it really works. I cover this concept in detail in Chapter 8.

Shying away from soaker hoses and mini-sprinklers

I've never been too fond of soaker hoses or mini-sprinklers. Here's why:

  • Soaker hoses are long tubes made of plastic or recycled rubber tires, connected to a faucet. Allegedly, they emit water along their entire length, saturating the soil directly beneath them. I've found, however, that all the water comes out in one or two places, usually in low spots. This happens because soaker hoses provide no internal control over the distribution of the water as drip systems do so well.
  • Mini-sprinklers are tiny sprinkler heads that are installed on drip tubing. Mini-sprinklers are fine for specialized applications, such as potted plants, some vegetable plantings, and very small areas. However, the mist they deliver is very fine, so it tends to blow away or evaporate before it reaches the soil. Also, the heads are fragile and easy to knock off kilter, resulting in uneven coverage.

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  • michael richter
    How to automate your irrigation?
    8 years ago

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